CVE-2020-26960: 
NixOS vulnerability analysis and mitigation

CVE-2020-26960 is a use-after-free vulnerability discovered in Mozilla Firefox, Firefox ESR, and Thunderbird that was disclosed on November 17, 2020. The vulnerability affects Firefox versions before 83, Firefox ESR versions before 78.5, and Thunderbird versions before 78.5. The issue occurs when the Compact() method is called on an nsTArray, where the array could be reallocated without updating other pointers (Mozilla Advisory, NVD).

The vulnerability stems from a memory management issue in the nsTArray implementation. When the Compact() method is called, it can trigger a reallocation of the array without properly updating all existing pointers to the array elements, leading to a potential use-after-free condition. The vulnerability has been assigned a CVSS v3.1 base score of 8.8 (High) with vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. The issue was identified as CWE-416: Use After Free (NVD).

The vulnerability could result in use-after-free memory corruption and potentially lead to an exploitable crash. While rated as having moderate impact by Mozilla, the vulnerability could potentially be exploited to execute arbitrary code if sufficient effort was applied (Mozilla Advisory).

The vulnerability was assessed as being very difficult to exploit, according to Mozilla's security team. No known exploits were reported in the wild at the time of disclosure (Mozilla Bug).

The vulnerability was fixed in Firefox 83, Firefox ESR 78.5, and Thunderbird 78.5. The fix involved modifying how the Compact() method handles array reallocation to prevent the use-after-free condition. Users should upgrade to these versions or later to mitigate the vulnerability (Mozilla Advisory).